The present invention relates to an automatic method for recognizing words embedded in connected speech.
From the beginning of the development of machine speech recognition, algorithms for performing speech recognition have been paced by the relative ability to implement them. As digital computers began to be used for speech research, however, the possibility of nonreal-time processing allowed algorithm development to outpace the capabilities available for real-time implementation. The 1970's were characterized on the one hand by increasing algorithmic complexity and on the other by considerable effort dedicated toward implementing cost-effective algorithms. The consumers of speech recognition technology have been caught in an unsatisfactory tradeoff between high performance speech recognition and low-cost implementation resulting in word recognition systems of marginal performance, excessive cost, and hence, dubious value.
In the past, microprocessors possessing sufficient computational power to process speech signals have been of special design--"custom IC's" . Examples of such processors are the "Speak & Spell" speech synthesizer chip and the various CCD and other analog speech analyzer chips. Now, however, another threshold of competency has been reached with the advent of programmable digital signal processors that are capable of performing a variety of functions including speech synthesis, word recognition, vocoding, voice verification, and even non-speech applications such as high-speed modems. The programmability of these signal processor chips is a very significant feature which overcomes two major problems with the development of special-purpose IC's for speech processing applications. First, the development cost for a special chip typically outweigh the market potential for such a chip (the "Speak & Spell" speech synthesizer was a notable exception), and second, lack of flexibility and "extensibility" of custom chips often minimize their useful lifetimes (especially considering the large development efforts required and the rapid development of speech processing technology). Furthermore, because of their programmability, a much broader market is created for programmable digital signal processor chips. Programmability has special importance for speech processing because of the relatively primitive stage of speech recognition algorithms. As the recognition technology is improved, some of these improvements may be incorporated through programming changes, rather than through system redefinition and redevelopment of integrated circuits.
It is now reasonable to plan for high-performance speech recognition systems based around these high-speed digital signal processor chips. These chips will perform all speech processing functions, including speech analysis and feature extraction, word recognition, pitch tracking, and speech synthesis using algorithms which have been identified as providing superior performance.